This application is related to and claims priority from Japanese Patent Applications No. 2000-294514 filed on Sep. 27, 2000 and No. 2001-101599 filed on Mar. 30, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a vehicle air conditioner including a heater core that uses waste heat generated in a heat pump cycle and a vehicle as a heating source, and it is suitably applied to an electric vehicle.
2. Description of Related Art
When a heating operation is performed in a conventional heat pump cycle (heat pump), it is well known that a surface of an exterior heat exchanger is frosted. However, when the heat pump is operated while the surface of the exterior heat exchanger is frosted, heat-absorbing efficiency of the exterior heat exchanger is deteriorated. In JP-A-10-166846, therefore, high-temperature refrigerant discharged from a compressor is supplied to the exterior heat exchanger to defrost the surface of the exterior heat exchanger. However, a heating operation cannot be performed while refrigerant discharged from the compressor is supplied to the exterior heat exchanger (i.e., during defrosting operation).
On the other hand, in JP-A-9-142139, when frosting on the surface of the exterior heat exchanger is detected, the frosting is restricted from proceeding by reducing an air amount blown to an interior heat exchanger or the like. Accordingly, a time of starting the defrosting operation is delayed, thereby lengthening a time (heating continuation time) for which a heating operation can be performed. When the operation of the heat pump cycle is continued while the surface of the exterior heat exchanger is frosted, the heat pump cycle is operated in a state where heat pump efficiency is degraded. Therefore, consumption power of the heat pump cycle (compressor) is increased.
Further, in JP-A-10-175415, a heater core using waste heat is provided in addition to the heat pump cycle, so that a heating operation can be performed even during a defrosting operation. In a vehicle, having a relatively small amount of waste heat, such as an electric vehicle, however, sufficient heating may be not obtained during the defrosting operation.
In view of the foregoing problems, it is an object of the present invention to provide a vehicle air conditioner which can obtain a sufficient heating even in a defrosting operation.
According to an aspect of the present invention, in a vehicle air conditioner, a heater pump cycle includes a compressor for compressing and discharging refrigerant, an interior heat exchanger for performing a heat exchange between refrigerant and air blown into a passenger compartment of the vehicle, and an exterior heat exchanger for performing a heat exchange between refrigerant and outside air outside the passenger compartment. A heat core is disposed for heating air blown into the passenger compartment by performing a heat exchange between air and a fluid which recovers waste heat generated in the vehicle. The vehicle air conditioner has frosting determination means for determining whether a surface of the exterior heat exchanger is frosted, heating capacity determining means for determining whether a heating capacity of the heater core is larger than a predetermined capacity, and a control unit for controlling operation of the heat pump cycle. In the vehicle air conditioner, at least when the frosting determination means determines a frosting on the surface of the exterior heat exchanger, and when the heating capacity determining means determines that the heating capacity of the heater core is larger than the predetermined capacity, the control unit performs a defrosting operation in which the surface of the exterior heat exchanger is defrosted. Accordingly, even in the defrosting operation, a sufficient heating can be obtained. Because the defrosting operation is performed while a sufficient heating is obtained, it can prevent the heat pump cycle from operating with a large power, and consumed power in the compressor can be reduced in the heating operation. In the present invention, when the heating capacity of the heater core is larger than the predetermined capacity, it can be determined that heating capacity of the heater core is sufficient for heating the passenger compartment.
According to an another aspect of the present invention, in a vehicle air conditioner, a ratio adjusting unit is disposed for adjusting a ratio of an air amount introduced through an inside air introduction port to an air amount introduced through an outside air introduction port, and frosting determination means for determining whether a surface of the exterior heat exchanger is frosted is provided. In this case, at least when the frosting determination means determines a frosting on the surface of the exterior heat exchanger, the control unit performs a defrosting operation in which the surface of the exterior heat exchanger is defrosted, and the ratio adjusting unit increases the ratio of the inside air amount introduced through the inside air introduction port. Accordingly, in the defrosting operation, a heat load of the heater core can be made smaller, and a sufficient heating can be obtained. That is, in the defrosting operation for defrosting the exterior heat exchanger, the heating capacity of the heater core is increased. In the present invention, the heating capacity of the heater core can be increased, by heating the fluid supplied to the heater core, by reducing a flow amount of the fluid, by increasing a rotation speed of an engine, by stopping operation of a blower for blowing outside air toward a radiator that cools the fluid, by increasing an output of a fuel cell, or the like.